For Cupcakes:Pre-heat oven to 325F. In a large bowl, mix together cake mix, flour, sugar, and salt. In the bowl of a mixer, mix together the egg whites, water, and vanilla. Mix on low for about 10 seconds. Slowly add the dry mix a little at a time. Mixing on low until everything is combined. Add sour cream and mix well. Add color now if desired. Mix well. Line a muffin/cupcake tin with paper liners. Fill each cupcake liner 3/4 full of batter. Bake at 325F for 25 minutes. Remove from oven and cool.For Royal Icing Flowers:In the bowl of a mixer, mix the warm water and the meringue powder. Mix for 30 seconds. Add the cream of tartar and mix for 30 seconds. Add powdered sugar slowly, mix until combined. Add in cornstarch and mix. Using the paddle attachment on the lowest speed, mix slowly for 10 minutes.Tint with gel food coloring. To Make the flowers: Fill a piping bag, fitted with a 2D Drop Flower Decorating Tip. On parchment paper, press tip to surface and squeeze, rotating your wrist from a 9'o'clock angle to a 12 o'clock angle. Release pressure and left away. Dot center with yellow icing. Let dry over night. Once flowers are dry, brush with edible glitter.Use to decorate cupcakesFor Cupcake Icing:For icing: Cream butter in the bowl of a mixer. Add cream cheese and mix well. Slowly add powdered sugar while mixing. Add vanilla and heavy cream and mix until combined. For my cupcake icing, I used a piping bag, fitted with a 2D Drop Flower Decorating Tip and swirled.